Re: Making a smart pointer which works with incomplete types

From:

Juha Nieminen <nospam@thanks.invalid>

Newsgroups:

comp.lang.c++

Date:

Sun, 07 Sep 2008 19:49:24 GMT

Message-ID:

<8fWwk.357$nL5.190@read4.inet.fi>

Alf P. Steinbach wrote:

* Juha Nieminen:

Alf P. Steinbach wrote:

<code file="x.cpp">
#include "sp.h"

class X;
X* newX();
void deleteX( X* );

int main()
{
SmartPtr<X, deleteX> p( newX() );
}
</code>

Here you require a "deleteX" function to be implemented by the user
alongside the X class,

No.

Yes you do. Your deleter template parameter is not optional.

and you require this "deleteX" function to be
given as template parameter to the smart pointer.

No. Well, yes, for this example code. But that's how example code goes,
it sort of needs to be concrete if it is to be any good to those who
don't understand.

Then show us the code which:

a) Doesn't require the user to explicitly define a deleter function for
each type.
b) Is able to properly delete the object based on an incomplete type.
(The smart pointer can require for the type to be complete at construction.)

Of course that works like that, but it's burdensome for the user to
have to do that for every single type he uses with the smart pointer.
The smart pointer ought to create such a function automatically to ease
the user's task, which is the whole point.

If the smart pointer can do that then AFAICS you're content to assume a
trivial destructor for the incomplete type, in which case you don't need
any special smart pointer type -- any will do.

I showed how to do it in my original post, and you don't need to
restrict yourself to trivial destructors.